linux-kernel - Re: [PATCH] x86, efi: Don't recursively acquire rtc

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Message-ID: <4E39D5DF.6010104@linux.intel.com>
Date:	Wed, 03 Aug 2011 16:12:31 -0700
From:	"H. Peter Anvin" <hpa@...ux.intel.com>
To:	Matt Fleming <matt@...sole-pimps.org>
CC:	linux-kernel@...r.kernel.org,
	Matt Fleming <matt.fleming@...ux.intel.com>,
	Jan Beulich <JBeulich@...ell.com>,
	Matthew Garrett <mjg@...hat.com>,
	Tony Luck <tony.luck@...el.com>,
	Fenghua Yu <fenghua.yu@...el.com>,
	Alessandro Zummo <a.zummo@...ertech.it>
Subject: Re: [PATCH] x86, efi: Don't recursively acquire rtc_lock

On 08/03/2011 02:04 PM, Matt Fleming wrote:
> From: Matt Fleming <matt.fleming@...ux.intel.com>
> 
> A deadlock was introduced on x86 in commit ef68c8f87ed1 ("x86:
> Serialize EFI time accesses on rtc_lock") because efi_get_time() and
> friends can be called with rtc_lock already held by
> read_persistent_time(), e.g.
> 
> timekeeping_init()
>     read_persistent_clock()	<-- acquire rtc_lock
>         efi_get_time()
>             phys_efi_get_time()	<-- acquire rtc_lock <DEADLOCK>
> 
> Move the locking up into the caller of efi.get_time() and provide some
> wrappers for use in other parts of the kernel instead of calling
> efi.get_time(), etc directly. This way we can hide the rtc_lock dance
> inside of arch/x86.
> 
> Cc: Jan Beulich <JBeulich@...ell.com>
> Cc: Matthew Garrett <mjg@...hat.com>
> Cc: "H. Peter Anvin" <hpa@...ux.intel.com>
> Cc: Tony Luck <tony.luck@...el.com>
> Cc: Fenghua Yu <fenghua.yu@...el.com>
> Cc: Alessandro Zummo <a.zummo@...ertech.it>
> Signed-off-by: Matt Fleming <matt.fleming@...ux.intel.com>

For the x86 footprint:

Acked-by: H. Peter Anvin <hpa@...ux.intel.com>
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